A currently widely available white LED is a device configured such that a blue emission LED is coated with a yellow phosphor using a down conversion process that employs a color conversion layer for a blue light source. In this regard, Nichia Corp., Japan, developed such a white LED by coating a blue LED made of gallium nitride (GaN) with a Y3Al5O12:Ce3+ (YAG:Ce) phosphor. However, the color thereof is difficult to control, and thus white light close to natural light fails to result, and color conversion depending upon changes in the ambient temperature is undesirably caused.
To overcome such problems, research and development into next-generation emission devices using LEDs and quantum dots is ongoing (S. Jeong et al., J. Phys. Chem. C 2010, 114, 14362; W. Zou et al., J. Mater. Chem. 2011, 21, 13276).
Quantum dots are semiconductor particles having as small a size as ones of nm, and have inherent light receiving/emitting properties. They have therefore been applied to medical imaging devices, solar cells, and emission devices. However, such quantum dots are problematic because the activity thereof is easily deteriorated due to contact with air, oxygen, or water. Hence, when quantum dots are used for emission devices, it is difficult to ensure emission stability.
Also, in order to confer the characteristic advantage of high crystallinity, quantum dots are synthesized in an organic solvent, but may be transferred to an aqueous solution depending on the application fields thereof. In this procedure, fluorescence yield may decrease.
Furthermore, in various application fields thereof, quantum dots are required to be in a solid phase, instead of a colloidal phase. When not in a colloidal phase, quantum dots may aggregate, which may have a negative influence on application thereof.